Western bean cutworm (WBC) adult moth catches are beginning to decrease for the majority of Ohio counties with an exception in Northeast Ohio. For week ending July 28, 18 counties monitored 63 traps (Figure 1). Overall, there was an average of 15 moths per trap (945 total captured). This is a decrease from an average of 25.1 moths/trap (1985 total captured) the previous week. Despite the general trend of adult moth catches decreasing, numbers suggest Northern Ohio counties should continue to scout for egg masses.
Figure 1. Average WBC adult per trap in Ohio counties, followed in parentheses by total number of traps monitored in each county for the week ending July 28, 2018. Legend (bottom right) describes the color coding on map for the average WBC per county.
Scouting and management. Scouting for egg masses should begin if there is one moth per trap per night. This would be indicated as an average of more than 7 moths per county (Figure 1). Female moths prefer to lay eggs in pre-tassel corn approaching tassel, so check such fields first. To scout for eggs or larvae (Figure 2), choose at least 20 consecutive plants in 5 random locations and inspect the uppermost 3–4 leaves for eggs, as well as the silks for larvae if tassel has emerged. Be sure to inspect different areas of the field that may be in different growth stages. Eggs are laid in unevenly distributed clusters of 5–200, but averaging about 50 per cluster, and hatch within 5–7 days. Eggs first appear white, then tan and then a dark purple. Once eggs turn purple, they will hatch within 24 to 48 hours. For field corn, if 8% or more of the plants inspected have eggs or larvae, consider treatment. For sweet corn, consider treatment if eggs or larvae are found on >4% of plants for the processing market or on >1% of plants for fresh-market. Bt corn with the Cry1F trait can no longer be relied upon for good WBC control, so these fields should be scouted too. These include Herculex I, Herculex Xtra, SmartStax, and others.
Figure 2. Top: WBC egg mass. Bottom: WBC larva.
If infestations exceed threshold, many insecticides are available to adequately control WBC, especially those containing a pyrethroid. However, as with any ear-burrowing caterpillar pest, timing is critical. Insecticide applications must occur after egg hatch, or after tassel emergence, but before caterpillars enter the ear. If eggs have hatched, applications should be made after 95% of the field has tassel. If eggs have not hatched, monitor for the color change. Hatch will occur within 24–48 hours once eggs turn purple. To search for larval injury after it has occurred, search the corn for ears having feeding holes on the outside of the husks.